Current cancer management options include chemotherapy, radiation therapy, surgery, immunotherapy, monoclonal antibody therapy and other experimental treatments. The treatment regimen is dependent upon the location and grade of the tumor, the stage of the disease and the health of the patient. Each treatment has its inherent benefits and limitations; some evoke more toxic side effects than others and some demonstrate better clinical efficacy than others. Enhancing T cell function in tumor-bearing hosts has recently gained therapeutic interest for its potential to overcome cancer-induced immune suppression. Recent clinical studies using monoclonal antibodies that enhance T cell function in cancer patients have shown significant anti-tumor efficacy in refractory melanoma, prostate cancer and renal carcinoma. OX40 (CD134) is a protein expressed on T cells that has shown therapeutic efficacy when targeted injected into mice with tumors. OX40 agonists enhance the immune system by stimulating T cells to infiltrate and kill tumor cells. Our group produced an OX40 mouse monoclonal antibody which showed intriguing properties in a Phase I clinical trial in Stage IV cancer patients. Agonox proposes to construct a humanized version of this antibody by using the antibody humanization company, BioAtla LLC, as a subcontractor. Benefits of antibody humanization include the absence of a human anti-mouse antibody (HAMA) response in treated patients that would thus enable clinicians to administer multiple doses in future cancer clinical trials most likely leading to enhanced clinical efficacy. Specific Aims in this proposal include further characterization of the mouse anti-human OX40 antibody variable regions for specificity of OX40 protein binding (ELISA and Western blot) and insertion of the variable regions from the antibody into an IgG backbone. After demonstrating binding of this re-engineered antibody to OX40 and confirming its biological activity, the anti-OX40 antibody will be humanized and retested for specificity, affinity and bioactivity. [humanization of the anti-OX40 antibody after insertion of the identical murine antibody's variable region CDR sequences into human IgG frameworks, assessment of OX40 binding and bioactivity in vitro, and development of a stably- transfected CHO cell line which produces a large quantity of the humanized anti-OX40 antibody for ultimate GMP production for a Phase I clinical trial in cancer patients.] Agonox, whose sole mission is the development of human OX40 agonists for use in cancer clinical trials, has been granted a royalty-bearing, exclusive license for the worldwide Intellectual Property rights to OX40 agonists in cancer immunotherapy from the Sisters of Providence in Oregon. Funding of this proposal will put us on the path to fulfilling ourthis mission. Successful completion of Phase I milestones will justify a Phase II award; funding would be used to create a stably-transfected, GMP-compliant cell line which produces the humanized Ab, concurrent with the establishment of a GMP Master Cell Bank to ensure availability of a sufficient supply for the life of the product, determine the antibody's optimal buffer formulation, have the humanized Ab manufactured and vialed under GMP, perform stability studies and sterility testing and perform pre-clinical toxicity studies (if necessary). Agonox has a team of translational clinicians and scientists with vast experience targeting OX40 in cancer. This team, along with an experienced humanization subcontractor, gives us hope that the humanized OX40 antibody will lead to a highly marketable, FDA-approved, biologic drug with high potential for enhancing T cell function and tumor regression in cancer patients.